Small plastic water tank next to freshwater pump

[High-pockets]

Exploring new to me 87 Excella 32’. While tracing water lines before energizing, I pulled up the floor of the closet and see the pump and adjacent to it is a small rectangular plastic tank. Water line from the pump appear to be plumbed into the tank. Any ideas? Looks original..

[High-pockets]

No replies but I think it was/is a winterization system

[GetawA-S]

If the pump goes to the tank (and it is a sturdy, sealed one) it may be an accumulator to dampen out the pulses from your diaphragm pump.
If the line goes from the tank to the pump, and there is access to add chemicals, then it is there for winterization purposes.

[High-pockets]

Thanks, I bite for winterization, thank you