Ontario Plumbing - Can a kitchen sink drain into a toilet trap arm?

Question

Struggling to come up with a solution for this. I'm located in Ontario, Canada.

Here is a diagram of the existing plumbing situation, as well as the new kitchen island sink I want to add. I am planning on using a loop vent, and have added most of the vent line already (connection higher than 36" on the stack, for example).

I was originally planning on tying the sink drain into the existing drain where marked, but now looking at the code again I think that would go against toilet trap arm rules, as the trap arm would then be serving both the toilet and the kitchen sink? Or it would effectively turn the kitchen drain into a toilet wet vent? Both of which are not allowed, I believe.

Or would it be ok since my kitchen island sink has its own trap arm?

Would appreciate advice on where to tie in the new kitchen sink drain line. Thank you!

PS. the old kitchen sink drain line was in the wall on the same line as the washroom sink, so it is not usable and I've closed it off now.

Answer 1

I’m not familiar with the Ontario Plumbing Code, but the National Plumbing Code of Canada (NPCC) mandates that when installing a wet vent, toilets must be installed downstream of all other fixtures (clause 2.5.2.1.d of NPCC).

Your existing configuration shows the toilet and the shower being wet-vented through the wash sink. However, the toilet is not the last fixture and it drains past the shower connection which would not be allowed.

If your local code allows a wet-vented toilet to be located upstream of the last fixture in the wet vent, then you could connect as you indicated in your sketch. This would result in a separately vented fixture being drained into a wet vent. The size of the wet vent would need to account for this load (table 2.5.8.1 of NPCC).

Otherwise, you would need to connect to the stack below the shower connection or repipe the shower so that it connects upstream of the toilet.