[Solved] Best Methods and Adapters for Recycling Sink Water into Toilet Flushing System

There is no simple off-the-shelf adapter; the practical low-cost approach is to use a shallow shower siphon under the sink and route the waste water to the toilet cistern with a hose or pipe, while accounting for sealing and overflow problems [#17958196] Sink siphons usually have small-diameter outlets, so a shower siphon is preferred because it is shallower and leaves more room for the small level difference between sink and cistern [#17958196] One proposed setup is to connect the hose from under the sink into the cistern inlet/side opening and set the float so the clean-water valve closes about halfway; the sink water then fills the rest of the tank, and any excess runs into the bowl [#17959759] Another suggestion was to use a reducer from the sink siphon to a hose and feed it into the cistern through the existing supply hole, avoiding a pump if gravity and height difference allow it [#17958009] Be aware that several replies warned about soap sludge, dirty deposits, possible clogging, and the toilet becoming harder to keep clean, especially with hard water [#17958618][#17960346]