Draw the trash slot by overlaying the bare trash can icon

over the single slot image instead of baking it in.

bags.lua

@@ -74,9 +74,9 @@ for bag_i = 1, 4 do
 			if ui.trash_enabled
 					or ui.is_creative(player_name)
 					or minetest.get_player_privs(player_name).give then
-				formspec[n] = "image[7.8,0.25;"..ui.imgscale..","..ui.imgscale..";ui_trash_slot.png]"
-						.. "list[detached:trash;main;7.95,0.25;1,1;]"
-				n = n + 1
+					formspec[n] = "image[7.8,0.25;"..ui.trash_slot_img.."]"
+					formspec[n+1] = "list[detached:trash;main;7.95,0.25;1,1;]"
+				n = n + 2
 			end
 			local inv = player:get_inventory()
 			for i = 1, 4 do

init.lua

@@ -102,6 +102,9 @@ for _, style in ipairs({ui.style_full, ui.style_lite}) do
                               ui.imgscale*8, ui.imgscale*4)
 end
 
+ui.trash_slot_img =         string.format("%f,%f;ui_single_slot.png^(ui_trash_slot_icon.png^[opacity:95)",
+                              ui.imgscale, ui.imgscale)
+
 -- Disable default creative inventory
 local creative = rawget(_G, "creative") or rawget(_G, "creative_inventory")
 if creative then

register.lua

@@ -187,8 +187,7 @@ ui.register_page("craft", {
 
 		if ui.trash_enabled or ui.is_creative(player_name) or minetest.get_player_privs(player_name).give then
 			formspec[n] = string.format("label[%f,%f;%s]", craftx + 6.45, crafty + 2.4, F(S("Trash:")))
-			formspec[n+1] = string.format("image[%f,%f;%f,%f;ui_trash_slot.png]",
-				craftx+6.25, crafty + 2.5, ui.imgscale, ui.imgscale)
+			formspec[n+1] = string.format("image[%f,%f;%s]", craftx+6.25, crafty + 2.5, ui.trash_slot_img)
 			formspec[n+2] = string.format("list[detached:trash;main;%f,%f;1,1;]", craftx + 6.4, crafty + 2.65)
 			n=n+3
 		end