There are four internal O-rings in the handle of your bypass assembly. To replace them, you'll need to depressurize the system and remove the safety clip.
Depressurize the Unit
1. Turn your main water supply off.
2. Drain the water lines by turning a faucet on at the highest and lowest points in the house. Leave these faucets open until they stop flowing.
Remove the O-rings
1. Remove the safety clip on the opposite side of the handle:
2. With a towel nearby, pull the handle out of the bypass assembly. You may need to pull out in a screwing motion, rotating the handle back and forth as you pull to release the O-ring seal.
3. Remove the four O-rings from the handle.
Install New O-rings and Repressurize
1. Lubricate the new O-rings and begin installing them, sliding them over the small end of the handle and securing them in the plastic channels.
2. Once all four new O-rings are installed, slide the handle back into the bypass assembly with that same screwing motion, being careful not to dislodge any of the rings.
3. Replace the safety clip back onto the end, and confirm the handle is pushed all the way in towards your plumbing.
4. Slowly turn on the main water supply, watching the bypass for leaks. Let the water run through your faucets until they reach a smooth flow with no sputtering or air bubbles.
5. Slowly open the bypass valve by pulling the handle out, stopping every few seconds to allow water back into the assembly.
6. Use water in the home as normal, and check for leaks over the next few days.