TWO Traps Necessary or Will ONE Work Safely?
spclark
| Posted in General Discussion on
Wife ordered new quartz countertops, new undermount stainless double bowl sink comes with.
Existing, similar sink has a disposal on one bowl, limited space in cabinet beneath; drains plumbed (by prior owner?) pretty weird, a bit lower than bottom of 1-1/2″ drain opening in wall behind.
Two traps (one sink bowl, other for disposal) feeding a sanitary T going downstream.
Once counter install’s complete & time for me to reconnect drains can I put one trap downstream from a T taking both sink and disposal discharge rather than replacing the two traps?
I’m comfortable doing it either way while at the same time intend to do a better job than what we were left with.
Replies
That's the way it is in our kitchen. The connection to the drain line needs to be fairly low, to accommodate the extra fittings.
Were I Working From Rough-in...
... I'd agree 100% Dan.
Problem is existing drain opening is pretty high on the wall, not as far beneath the sink bottom as I'd like to have it for both disposal and secondary sink bowl combined discharge.
If 2 traps are 'normal' I can do that better than what I started with but 1 trap'd be easier.
Pic = 1,000 words
OK so I've located a manual for the disposal unit I intend to re-install, it says separate traps are necessary if there's another sink to be connected. Oh well....
Did learn there's a dishwasher discharge inlet built into the disposal that may help. Right now DW's discharge goes into second sink's drain. If I re-route that to the disposal I can raise the trap for the second sink a few inches, recover some space under that sink that'd otherwise go for drain plumbing.
Additional flow thru the disposal ought to keep it cleaner?
Yeah, it's pretty normal to route the DW into the disposal.
Continuous Waste
With a continuous waste use only one trap. The best and cleanest installation if you have access to the plumbing in the wall behind the sink is to install a drain inlet directly behind each sink bowl, each as high as possible (as determined by your disposer). Attach each sink bowl with it's own trap going directly back to its inlet. The last time I redid my kitchen I used this installation. I'd post a picture, but I'm on another continent. The space under the sink is more usable, not being cluttered up with a bunch crap. This set up is much less likely to clog. A single vent can serve both sinks. I think the only reason that this is not the norm is that the exact location of the sink needs to be known at plumbing rough-in, which is seldom possible.
Done...
... with no leaks.
Adding a second drain inlet wouldabeen OVERKILL for this project though I admit that's have been my choice were I doing a rough-in.
Turned out doing two traps wasn't quite as bad as I'd expected. Biggest unknown when I started this thread was how the new double bowl SS sink that came with the new counter top(s) would be configured. When everything arrived last Monday I saw the bowl that'd be taking the disposal was shallower than the other one, which actually helped.
Having both bowl drains closer to the wall behind (off center fore-n-aft) than the old sink made me a little uneasy as the drain inlet is directly behind the disposal sink drain. Duplex outlet for dishwasher and disposal is too close to the drain inlet for my comfort too, yet one more reason for ripping out the old work & adding a second inlet & moving that box to a different location.
That all's gonna wait for the day I move the under-floor drain line out away from the foundation wall a couple of feet; right now it's hard against the wall & routed directly over the main breaker panel... not something I like either.
Anyway, attached pic shows the completed installation. Left sink trap outlet's higher than disposal trap outlet, disposal discharge higher than drain inlet in wall by about 1-1/2". Shouldn't have water standing anywhere in new drain but the traps.