Most turn down my request to shower together. I understand sometimes because I'm pretty big and fitting another guy with me in a shower is difficult. One masseur told me he didn't feel like showering again because he showered so many times in a day already, once before each session.
I have showered with masseurs twice.
Once was after a 4 handed session with a Latino couple in Long Beach. The smaller and younger of the two, spoke little English, washed all of me down in the shower after while I chatted with his boyfriend about how lucky he was as to have the younger guy as a partner.
The other was after a body gliding session. We both needed to rinse various fluids from our bodies. It was very normal because we were both able to have basic conversation as we washed off the lube and fondled each other a little more.