The SC Protium 3.0 Reservoir Coupler is for combining multiple Protium Reservoirs. It is compatible with any Protium Reservoir, D5/Reservoir Combination or Reservoir Tube. We had many requests for long reservoir tubes beyond the longest size we provide, which is 250mm. This product is for larger cases where large reservoir volume is desired,
Purchase Protium 3.0 Reservoir Coupler
https://singularitycomputers.com/shop/watercooling/protium-accessories/protium-3-0-reservoir-coupler