so i was bored lol
this might give you some ideas
black is 2x4's
green plumbing
red sump
i would make it strong so you can stand on it.
2x4 framing.
the top 2x4's put on top of the sides.
on the top,im not sure how big this thing is so 3 or 4 pieces wide,whatever looks good.
if you want the top stronger,turn the 2x4's up.
few corner cross braces
on the back i would do like in pic
leave out the center so you can lift the bench off and not hit the pipes.
but still do the back 2 sides for strength.
after all that i would skin it with some plywood.
then add some wood corner bead.
then use some 1 step stain & polyurethane to finish it.
that would be tight

if this helped,good,if not,oh well.

good luck
show lots of pix
