Ok, done.

code/modules/recycling/conveyor2.dm

@@ -252,7 +252,7 @@ GLOBAL_LIST_EMPTY(conveyors_by_id)
 
 // update the icon depending on the position
 
-/obj/machinery/conveyor_switch/update_icon()
+/obj/machinery/conveyor_switch/update_icon_state()
 	if(position<0)
 		if(invert_icon)
 			icon_state = "switch-fwd"

code/modules/recycling/disposal/bin.dm

@@ -191,10 +191,6 @@
 		AM.pipe_eject(0)
 	update_icon()
 
-// update the icon & overlays to reflect mode & status
-/obj/machinery/disposal/update_icon()
-	return
-
 /obj/machinery/disposal/proc/flush()
 	flushing = TRUE
 	flushAnimation()
@@ -386,8 +382,8 @@
 	pressure_charging = TRUE
 	update_icon()
 
-/obj/machinery/disposal/bin/update_icon()
-	cut_overlays()
+/obj/machinery/disposal/bin/update_overlays()
+	. = ..()
 	if(stat & BROKEN)
 		pressure_charging = FALSE
 		flush = FALSE
@@ -395,7 +391,7 @@
 
 	//flush handle
 	if(flush)
-		add_overlay("dispover-handle")
+		. += "dispover-handle"
 
 	//only handle is shown if no power
 	if(stat & NOPOWER || panel_open)
@@ -403,13 +399,13 @@
 
 	//check for items in disposal - occupied light
 	if(contents.len > 0)
-		add_overlay("dispover-full")
+		. += "dispover-full"
 
 	//charging and ready light
 	if(pressure_charging)
-		add_overlay("dispover-charge")
+		. += "dispover-charge"
 	else if(full_pressure)
-		add_overlay("dispover-ready")
+		. += "dispover-ready"
 
 /obj/machinery/disposal/bin/proc/do_flush()
 	set waitfor = FALSE