I did this mod last year on my ST30BH, so will attempt to remember the details as my trailer is at the storage lot 30 miles away and can't send a picture. Pretty sure the elbow I used was 1/2". Bought that, the end drain valve,a few feet of clear plastic tubing, and 3 or 4 clamps to hold the tubing in place. Being as I couldn't run the tube straight out from the drain to the side due to the slide, I threaded it through a hole associated with the wheels (I think) then along the underside to where I could removea bolt that held the trim piece to the fabric of the underbelly, place a clamp in the same hole and reattach the bolt. I think I used 3 or 4 clamps along that lineto extend the tubing to near where the holding tank valves are. I cut the end of the tubing flush with the last clamp so the drain valve would be snug with the clamp and the tubing would not sag. Minimal time, minimal cost. So far, so good. Got tired of getting my shirts, pants, knees dirty crawling under the trailer to remove the original drain cap.
Hope this makes sense. Ask away if any questions.
'08 Crossroads Sunset Trail ST30BH Traded
'21 Grand Design Reflection 31MB 5er
'22 Cougar 29RLI 5er
'14 RAM 2500 4X4 CTD