Are there 3-way water pipe junctions which allow any variant of flow?
Get a 1-1/4&quot; PVC T-fitting.  They're cheap.
Cast &quot;Detect magic&quot; on it.  There's no magic.  (magical T-fittings are NOT cheap).
Now look at the device itself with the Mark 1 eyeball and Fingers 1.0.
Do you see anything special about that fitting?
No. There are no innards/guts which would provide any sort of flow checking.  If you want, you can also examine a check valve to see an example of a piece which does have flow-management innards.
So a plain &quot;tee&quot; is &quot;exactly what it says on the tin&quot;.  Flow will be decided by whatever is connected to it and how.