The shower is in my basement & The drain goes to a tank in the slab for up-flush..

Shower should be vented after P-Trap. In other words, water enters P-Trap first then flows pass the vent.

Yes Milo is correct vent is after the P-Trap see the attachment for vent lay out, Thanks.

John

Both experts are correct. The vent runs after the trap. However, there.s another way that doesn't involve running a vent off the shower as depicted in the image john put up. We wet vent , (see image ) our showers in my area. This reduces the number of bathroom roof vents from three to one. Your choice. Tom