Sometimes put rings dropped into sinks in the pipes

aka bury the ring under the sink. Idea from Fredrik Ljungdahl.

doc/fixes36.1

@@ -462,6 +462,7 @@ when poly'd into a giant and moving onto a boulder's spot, you could get "you
 	it up", "you are carrying too much stuff to pick up another boulder"
 improve #adjust command's handling of the '$' and '#' inventory slots
 prevent #adjust from allowing anything to be moved into the special '-' slot
+sometimes rings dropped into sinks can be found in the pipes
 
 
 Fixes to Post-3.6.0 Problems that Were Exposed Via git Repository

src/do.c

@@ -501,6 +501,12 @@ register struct obj *obj;
         pline_The("sink backs up, leaving %s.", doname(obj));
         obj->in_use = FALSE;
         dropx(obj);
+    } else if (!rn2(5)) {
+        freeinv(obj);
+        obj->in_use = FALSE;
+        obj->ox = u.ux;
+        obj->oy = u.uy;
+        add_to_buried(obj);
     } else
         useup(obj);
 }