Take the RV to a certified dump station found at campgrounds and some interstate rest areas. Pump out all waste and water from the existing black water tank. Drive the RV to your parking lot, set the emergency brake and disconnect all water and electric connections to the rig.
Open the black water tank panel, typically found in the rear left side of the RV's exterior. Put on gloves, mask and safety goggles to prevent contamination. Use pliers to remove the hose from the back of the existing black water tank. Pull the old tank out and place the new one into the holding area.
Go inside the RV to the toilet and check the hose connection on the back of the bowl. Push the hose out from the toilet so it extends into the holding area beside the new black water tank.
Slide a new hose clamp over the end of the hose coming out from the toilet and then connect the hose to the nozzle on the new black water tank. Tighten the hose clamp so it rests tightly over the hose and black water tank nozzle.
Apply a coat of silicone caulk around the end of the hose at the black water tank to provide additional waterproofing to the connection. Add a coating of the silicone caulk to the toilet's hose connection inside the RV as well.
Reconnect the water to the RV. Test the flushing and water flow to the black water tank by flushing the toilet once or twice.