wwhitney
In the Trades
A wet vent is when a pipe acts both as a drain for upstream fixtures and a vent for downstream fixtures.
For example, in your drawing in post #3, I interpret that there's a vertical pipe which is a dry vent on top, the lav connects, and then the tub trap arm connects, then it ties into a horizontal drain. The pie between the lav connections and the tub connection is a vertical wet vent--the pipe is a drain for the lav and a vent for the tub.
If I understand the layout correctly, the WC at the bottom of that drawing is currently horizontally wet vented by the lav. A horizontal wet vent can only carry bathroom fixtures, so if you connect the washer where it shows in post #3, you disrupt the horizontal wet venting of the WC. The WC ends up unvented, so that's not good.
If you can tie the washer in downstream of the WC, that works.
Not sure I addressed all your questions, I've lost track a bit since the post #3 diagram. If you have more questions, particularly about an arrangement different from post #3, an updated diagram would help.
As to the slope of the horizontals, for a vented drain, as I commented you can have extra slope if you want. 1/2" per foot, 1" per foot, 30 degrees above horizontal, etc. On a trap arm, the drain between a trap and its vent, you are limited to one pipe diameter of fall, to avoid siphoning the trap. So there it is typically best to stick to 1/4" per foot. On a very short trap arm you could afford a little more slope if necessary for some reason.
Cheers, Wayne
For example, in your drawing in post #3, I interpret that there's a vertical pipe which is a dry vent on top, the lav connects, and then the tub trap arm connects, then it ties into a horizontal drain. The pie between the lav connections and the tub connection is a vertical wet vent--the pipe is a drain for the lav and a vent for the tub.
If I understand the layout correctly, the WC at the bottom of that drawing is currently horizontally wet vented by the lav. A horizontal wet vent can only carry bathroom fixtures, so if you connect the washer where it shows in post #3, you disrupt the horizontal wet venting of the WC. The WC ends up unvented, so that's not good.
If you can tie the washer in downstream of the WC, that works.
Not sure I addressed all your questions, I've lost track a bit since the post #3 diagram. If you have more questions, particularly about an arrangement different from post #3, an updated diagram would help.
As to the slope of the horizontals, for a vented drain, as I commented you can have extra slope if you want. 1/2" per foot, 1" per foot, 30 degrees above horizontal, etc. On a trap arm, the drain between a trap and its vent, you are limited to one pipe diameter of fall, to avoid siphoning the trap. So there it is typically best to stick to 1/4" per foot. On a very short trap arm you could afford a little more slope if necessary for some reason.
Cheers, Wayne