Planning to add toilet to basement... someone said you should not cut out section of floor to put drain underneath because when you add concrete back into that area the new concrete will not adhere to the old concrete and you will create a future water problem with water seeping up through the cracks... is that true ? I'd rather not have to put toilet up on a raised platform or have to buy an expense flush-up unit. What is the best solution ?
Thanks

Someone was wrong, we do it all of the time. Does your existing main drain leave the home under the floor or through the side wall above the floor?

It is under the floor

It is under the floor

Countless people take up concrete to install toilets. If your plumbing is done right and the ground is well drained all around the house, and you mix the concrete right, and wet around the edges of the old concrete, and let it dry enough, and it isn't too cold out - you should be OK.

UNFAIR NEGATIVE.
Nowhere do you say 'it us under the floor' and negatives shouldn't be tossed out like candy anyway/
Did you read the rules?

I felt the same way so I popped a green button.

I fully appreciate joypulv and ma0641's comments and balancer. You said nothing about your existing sewer line and "under the floor" is no where in your post so why the bad rating? If you want folks to help you try not jerking us around and please read the rules for rating. The old version of AMHD would have prevented a newby like yourself from raing anybody until you had used the desk for some time. You are using the new "skin" version so they let you rate, another AMHD mistake in my mind.

I appologize... very sorry... being a newby I misunderstood the symbols... it was not meant to be a negative feedback... I thought I was giving a positive... actually I didn't see a symbol for positive... again probably because I am first time user.

OK... I responded to your original answer twice saying "it is under the floor" I have to assume that you did not get those messages... then, being a newby, I saw the feedback button (not realizing it was a negative) and sent a message assuming that my first 2 didn't get through... "it is under the floor"... after I saw the comments about what I did... I went to look for instruction on feedback... I don't see anything...
Anyway I certainly appologize... I had no idea that I was giving negative feedback... I was only trying to get my question through to you... very very sorry...
You have to understand that a person with a question who looks for answers and finds this site... generally will not think about looking for all of the rules first... most would do as I did... ask and hope to get a good answer... sorry again.

I understand better now and no hard feeling. One of the recent changes the owners of the site created is causing this problem for new folks. Back to your situation, yes you can cut the concrete or better yet jack hammer it out. There will be little trouble getting the new crete to adhere to the old.

Just to back up all above answers, yes, cutting or breaking up concrete and doing the tie in under the concrete is the correct way to do you toilet drain install. We are constantly breaking up crete to rough in basement bathrooms and pour and finish our own concrete on these jobs. Never had a problem with water. This is the standard for plumbers, has been forever, and always will be. Good luck with your project. Take care.

PS. You could always seal the concrete just to be double safe.