How To Deal With Hydrogen Peroxide After De-Yellowing?
After doing a simple search, it seems that the general consensus is, it's okay to pour the used amount down the drain.  

Most of us get it.  The stuff's been sitting in your house taking up space, and because of the unfamiliarity with this chemical, you and environmentally conscious thinkers such as yourself, would never want to further harm our shared environment.

Bottom line: No new bubbles means no more potency, the green light to pour away.