Can I run a toilet and a shower underground into a floor drain about six feet away from both fixtures and if so are floor drains already vented

Floor drains are not sewers and can not be used as such. Does your floor drain go to a sump pump. Septci tank or city sewer? Does you sewer main leave the basement through the wall or through the floor?

No pumps its city sewer and it is underground I don't see why you couldn't use it it's a four inch pipe I'm pretty sure its not vented but I will vent shower and toilet through ceiling joists its only about 15 feet away so at an 1/4 per 10 feet there should be plenty of room up there for proper slope but why couldn't I just tie in to that drain if its already 4 inch underground and its about a foot and a half down so there is enough room for slope the shower and toilet are about 6 feet away from that drain
If I dig up the floor can I run a toilet and a shower to the existing floor drain its got to be vented already right

4' pipe does not require 1/4" slope, everything smaller does. You only need a 1/8" slope. Are you certain your floor drain goes to city sewer? That would be quite rare. Most cities sewer is separate from storm and drain water, sewer plants do not like to waste treatment volume on drain water

It's the vent pipe which would be 2 inch for the 1/4 inch slope. 2 inch would be like right what I need I think 4 inch would be over kill for a vent do you agree. Well I haven't torn up the floor yet but that drain is tied in to the same line as the drain for the kitchen sink so I just assumed. We all know what happens when we assume. OK well maybe I have to start ripping up some concrete to see where the pipe from the other bathrooms is going that's on the other side of the basement those go underground as well.

Yes 4" for a vent is a waste in your case. I must have misread and thought you were adding a 4" drain over to your floor drain.

Hi Louie

You asked, "Can I run a toilet and a shower underground into a floor drain"?

Did you plan on ripping out the floor drain? Here, if you rip out the 4" floor drain then there should be no issue with connecting to that drain line (as long as connected to the sewer, of course).

You will still need to run a 2" vent for the sink even if the floor drain is vented... sink MUST be vented and that vent will WET VENT the toilet.

Finally, if you have a main drain clean out and can remove the cap and can see inside the pipe I'd set a running hose down the floor drain and see if you can see water flow past the cap to confirm sewer connection.

Back to you...

Mark

Ty mark I will get back on when I tear out the floor Thurs.

Understood!

Can I run a toilet and a shower underground into a floor drain about six feet away from both fixtures and if so are floor drains already vented
No you can't tie a bathroom group to an floor drain and no they aren't vented, You will have to open up the slab and cut in a wye or combo to pick up your group. A 2" vent will have to be installed although if AAVs (air admittance vents) are allowed you may install one of those. Here's a typical bathroom rough in using a wet vent. Good luck. Tom

No you can't tie a bathroom group to an floor drain and no they aren't vented, You will have to open up the slab and cut in a wye or combo to pick up your group. A 2" vent will have to be installed although if AAVs (air admittance vents) are allowed you may install one of those. Here's a typical bathroom rough in using a wet vent. Good luck. Tom

Ty for that I'm changinging the location to directly under the first floor bathroom my sewage pipe is now about two feet away and it's a 4 inch cast iron pipe goinginto the slab it looks like that's also the vent pipe. Could that be true if so all I have to do is run my plumbing into that pipe and that takes care of everything or what sorry to be a pain but just need to educate myself as much as possible before I start ty.

Hi Louie

If anything from upstairs drains into that pipe then you CANNOT use the pipe as a vent. You can, however, cut into the stack and take a fitting off for the future bath. The sink would still need the 2" vent and that would act as the toilet wet vent as mentioned earlier. The 2" vent would need to connect into a 2" or larger vent in the basement or go upstairs and connect into a 2" or larger vent a minimum of 42" above the floor or the 2" vent could penetrate the roof by itself.

Now I'm confused there's already a second floor and a first floor bathroom sharing this pipe so why can't I use it for the plumbing in the basement. And there's no other pipes it's that same pipe that goes through the roof of the house so there using the sewage drain pipe as the vent pipe also so just to be clear there's a 4inch cast iron pipe from under the concrete floor and it extends through the roof of the house. There's two full bathrooms tied into this pipe on the first and second floor I can hear water running through this pipe when at any fixture in any of the bathrooms. Just trying to figure this out thanks for the feed back

You can use the pipe as a drain, but you can't use the stack as a vent. Here, when sewer waste passes by an unvented fixture on a lower floor... which yours would be if you didn't add vent... it will create suction and unless that suction is relieved it will vent through the fixtures causing burping action which will allow sewer gasses into your home.

Your fixtures on the first floor have a vent, but the upstairs plumbing may in fact use the 4" pipe as a vent and that would be OK 'cause no fixtures above the 2nd floor. The first floor, however, must have some kind of vent or the plumbing wasn't done to code... ;)

Let me know if all that makes sense, OK?

You can use the pipe as a drain, but you can't use the stack as a vent. Here, when sewer waste passes by an unvented fixture on a lower floor...which yours would be if you didn't add an additional vent...it will create suction and unless that suction is relieved it will vent through the fixtures causing burping action which will allow sewer gasses into your home.

Your fixtures on the first floor have a vent, but the upstairs plumbing may in fact use the 4" pipe as a vent and that would be OK 'cause no fixtures above the 2nd floor. the first floor, however, must have some kind of vent or the plumbing wasn't done to code...;)

Let me know if all that makes sense, OK?
OK so I have to locate vent from first floor OK well I'm taking up the concrete tomorrow and I'll look for vent worst case scenario I can't tie into it I can run a new one through the outside wall up the outside of the house as long as its above roof line correct. Thank you very much and do you by chance have a venting diagram for something like that or does the previous still apply

OK the vent from the first floor did tie into that 4 inch pipe but it tied in above the second floor fixtures I have trench dug I think I'm in pretty good shape now my shower 2 inch connects to toilet four inch then goes into 6 inch main where along that line do I tie in the vents ex. Shower drain trap then vent or shower drain vent then trap then on toilet I'm guessing on the street 90 before it hits the main correct. Now the sink is on the opposite end of bathroom still draining into same drain just at a different location do I still need to vent that as well. I don't know what wet venting is I thought that was the job of the trap,am Iwrong. Ty your very helpful

Ty for that I'm changinging the location to directly under the first floor bathroom my sewage pipe is now about two feet away and its a 4 inch cast iron pipe goinginto the slab it looks like that's also the vent pipe. Could that be true if so all I have to do is run my plumbing into that pipe and that takes care of everything or what sorry to be a pain but just need to educate myself as much as possible before I start ty.

Massplumber shot that down. My diagram shows a typical wet vent, You do have options here.
1- Run a new vent out the roof
2. Run to the attic and connect to a existing roof vent.
3- Connect to another fixtures dry vent connecting at least 6" over that fixtures flood rim. **OR**
4- If AAVs (air admittance vents) are allowed in your area you can install a Studore Vent, (see image)
Good luck. Tom

Wet venting has nothing to do with the ptrap. Wet venting is when the drain/vent from one fixture vents another fixture (or more). In your case, you want to have the sink/drain vent WET VENT the shower and the toilet.

Speedball posted a diagram of how to pipe this all up in post #10... see above. The sink/drain vent comes off the shower drain and it is this sink vent that will vent the other fixtures. The sink drain and vent must remain 2" until it can connect into a 2" or larger vent upstairs or, if mechanical vents are allowed, an AAV (mechanical vent... see Tom's post above) can be installed under the sink off the sink vent.

Mark