duct tape and leaky dishwasher

We just moved into a new house. We noticed some water damage under the sink before we moved in, but had never experienced a leak first hand until tonight. it seems that the dishwasher when draining caused a backup under the cabinet.

upon further review, i noticed that their is a drain cap under the sink. but the cap is on a Y and only 1 of the 2 branches are "capped," the other side was just covered by duct tape. It was wet around this area, and when i peeled the duct tape back, it was filled with a dark sediment.

can i or should i place a pvc cap over this duct taped piece. do i need to open up this cap and clean this area out? would i just snake it?

we are on a well and septic if that makes a difference.

i have attached 2 pictures so i hope that this helps.

Yes I would cap that!

Must not have done a home inspection, or had a plumbing inspection.

The first plumber never finished the job there.

Believe it or not, Duct Tape is not a plumbing product.

pipe

YOu already have a cleanout opening there, so just install a short piece of pipe and a cap into the opening. Regardless of what some say, "The universe runs on duct tape", it will not prevent leaks in plumbing pipes. The drain line may also require cleaning if the leak is caused by a backup.