I have a portable dehumidifier that has a pump that I'm looking to connect its 1/4" tube to my PVC waste line. The waste line already has a Y connector that has a black rubber cap on it. I'd like to tie in there but my concern is a backup. I once removed the black cap we. The sink upstairs wouldn't drain and water came gushing out. Once I snaked the line it was ok. If this happens again I'm afraid water will back up here and damage the dehumidifier or cause a leak. Is there a preferred way to connect it so it will not backup and ruin dehumidifier? Do I need a trap and a check valve?

is there a washing machine standpipe nearby? drain the 1/4 inch tube into it.
if not... it should discharge into a properly vented trap. you keep sewer back ups from going into the 1/4 tube by keeping an air gap between the tube and the drain fitting.

I don't have a washing machine in the basement. So all I need is to have tube drain into a trap with an actual connection? Just put tube in pipe similar to a washing machine hose? And to prevent any backup should I ise a check valve of some sort?

You can't stop a drain from backing up, so you have to prevent the possibility of a backup from touching the drain, and be above the flood level rim of the trap by a minimum of an inch.

most condensate pumps have a built in check valve. i don't know about a dehumidifier pump? it may as well??

check valve is a good thing


STILL REQUIRES an air gap before drain


REQUIRES

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

In doing this, if the sewer line backs up again sewage will come out of the open line.

YES

precisely

but it will NOT enter the dehumidifier

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

So is there anyway to prevent a backup from coming out the open drain?

No. If a backup occurs, it will flood out the lowest point in the system after the stoppage. Using an air gap is the only reliable and approved way to protect yourself.