I use Zoot 9" trishorts (thin liner), under Champion (Walmart & other retailers) swim trunks (drys quickly & was what I had laying around the house one day so I tried it & it makes a decent gym short) 38" waist size L works for me

1st pic is the swim trunks, 2nd pic is the trishorts I have (I use them on the bike but also in the gym, it helps with moisture management cuz I have hyperhidrosis) (tip: get a big size for max comfort size XXL works for my 38"waist)

on the bike I wear MTB shorts over the trishorts (check out ZOIC Ether Shorts - No Liner - Men's, size XXL) 3rd pic