My downstairs bathroom used to also be the laundry room, but I have relocated the laundry room. I am looking at adding either a tub or a shower unit to the bathroom. Can I covert the old washer drain into a tub drain? I am trying to avoid digging up concrete.

"I am looking at adding either a tub or a shower unit to the bathroom. Can i covert the old washer drain into a tub drain? I am trying to avoid digging up concrete."

Since both bath tub and shower base traps install under the floor about the only way you're going to accomplish this is to platform the tub or shower and raise it up up high enough to drain into the washer drain pipe. Since water will not drain uphill there just aren't any other options. Sorry, tom

Would I be able to use a 1 1/2 inch trap for a tub? I figure I would have to build a platform, about 4 inches total height for a tub to put the trap under.. to do similarly for the shower I would have to have a 8 inch platform for a 2" or a 7 inch platform for 1 1/2" (it would have to be in another corner due to the furnace pipes reducing the ceiling level right above the used-to-be washer drain.)

Would I need to run a vent line?

would i be able to use a 1 1/2 inch trap for a tub? i figure i would have to build a platform, about 4 inches total height for a tub to put the trap under.. to do similarly for the shower I would have to have a 8 inch platform for a 2" or a 7 inch platform for 1 1/2" (it would have to be in another corner due to the furnace pipes reducing the ceiling level right above the used-to-be washer drain.)

would i need to run a vent line?

Use the 1 1/2" trap and drain line. That's how we used to rough them in the old days. If you connect the drain to the drainage tee in the washer line you're already vented. Good luck, Tom