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Washing Machine Drain Design
We are putting a washing machine in the basement. The copper supply lines were pretty straightforward to add to our system, but I have some questions about the waste line design. As we get further into it, we've been wondering if our original design is too simplistic.
There is an existing large basin utility sink that is near the washing machine location, and it has a 1-1/2" drain line. There is one trap right beside the main, and a second trap under the sink. The sink is approximately 7 feet from the main. The washing machine is about 15 feet from the main, and you would go past the sink to get to the washing machine. I drew a simple sketch of the system and attached it.
Unfortunately, it is very cluttered on the main near the floor, so if we tap into the main again, the tie point would be a minimum of 32" off the floor and it would be a really big hassle to support the pipe as it would run behind the HVAC, water softener, sink at a really bad height. So, we would prefer to utilize the existing 1-1/2" tie point that the sink uses, and tie in upstream of the trap right off the main. Since it is just a utility sink, it isn't the end of the world if both can't drain at the same time, or if the sink serves as a slight surge basin for the washer.
Final trick to this line: there is a tee in the 1-1/2" line about 6" off the floor (shown in red on my drawing) that is just open to our basement. It is upstream of the trap, so it doesn't let sewer gas into the basement or anything that we've ever smelled. The condensate line from the HVAC and the drain from the water softener sit in that open line so that they can gravity drain. Right now, in the event that either of those connections pops out of the riser, or you try to drain a sink full of water, those connections are right beside some wooden shelves in a really crummy spot to have water on the floor. Being that the open pipe isn't even as high as the *bottom* of the sink, this is just trouble that I'm not sure why someone ever set up to happen.
My questions are:
1. While I know it may not be ideal, will it be legal and acceptable to tie the washer into the existing 1-1/2" drain line connection to the main? We would tie in on the upstream side of the 1-1/2" trap that is right off the main line.
2: Do we need a new vent for the washer (and utility sink too I guess), or does the trap right by the main adequately protect the system because it is in such close proximity to the 4" main?
2.5: I assume the main is vented, but haven't gone to verify this in the attic or anything. Is that a safe assumption?
3: If we put in a riser so that the condensate line from the HVAC and drain from the water softener are higher than the sink but still gravity draining (they would be approximately level with the washer standpipe), is that going to be a problem? I would actually prefer to make more like hard connections with an airbreak directed to a place where I could manage any overflow OK (aka the sump area). I would do this by putting in a riser with a cross on the top, then hardpiping the condensate and water softener drain to the horizontals on the cross, then running an piece of PVC off the top of the cross down to the sump area about 10 feet away. I would leave the piece of PVC to the sump open on the end to provide an air break in the riser to prevent stuff from sucking into the HVAC or water softener. Our sump pit is sealed, but it is still the low point in the basement and a much easier place to clean up any water problems.
4: If the answer to #1 is no, then would it be OK to tap into the main 32" off the floor, put a 2-1/2" trap right by the main, run a 2-1/2" pipe 15 feet over to the washer (the pipe would barely be able to slope toward the drain at all), dip straight down a foot or so at the end to a U, then come straight up into a 2" standpipe for the washer? The top of the standpipe would be about 41" off the ground.
