Humiliation at Masters home

I have served a husband and wife for about 18 years as their naked houseboy and they enjoy humiliation along with discipline and other activities. When I stay over I am at night chained to the sofa bed naked on my back without any sheet to cover me.
Come the morning I usually have a morning wood erection which means she sees everything when she comes into release me.
On occassions I have needed to urinate and this is clear to them when I am released and have to clean up my mess.