Heater Hose for waste tank boxes

[Retodded]

Can anyone tell me what the configuration is for the grey and black tank box heater hoses? I know they go into the side of the boxes and I know that one long hose comes from the floor on the curb side of the trailer and goes into the black tank box but where does the grey tank hose come from???

pics would be awesome...

p.s. I had a 50/50 shot as to whether this was better posted in wastes systems or heater section.

Thanks in advance

Todd

1975 sovereign 31ft