diff --git a/basis/liquid_lib.lua b/basis/liquid_lib.lua
index 5b51440..bf1c395 100644
--- a/basis/liquid_lib.lua
+++ b/basis/liquid_lib.lua
@@ -38,21 +38,18 @@ function techage.liquid.formspec(pos, nvm)
 	end
 	local name = minetest.get_node(pos).name
 	if name == "techage:ta4_tank" then
-		local public = dump((M(pos):get_int("public") or 0) == 1)
-		return "size[5,3]"..
-			default.gui_bg..
-			default.gui_bg_img..
-			default.gui_slots..
+		local meta = M(pos)
+		local public = dump((meta:get_int("public") or 0) == 1)
+		local keep_assignment = dump((meta:get_int("keep_assignment") or 0) == 1)
+		return "size[5,3.5]"..
 			"box[0,-0.1;4.8,0.5;#c6e8ff]"..
 			"label[1.5,-0.1;"..minetest.colorize("#000000", title).."]"..
 			help(4.4, -0.1)..
 			techage.item_image(2, 1, itemname)..
-			"checkbox[0.1,2.5;public;"..S("Allow public access to the tank")..";"..public.."]"
+			"checkbox[0.1,2.5;public;"..S("Allow public access to the tank")..";"..public.."]"..
+			"checkbox[0.1,3;keep_assignment;"..S("keep assignment")..";"..keep_assignment.."]"
 	else
 		return "size[4,2]"..
-			default.gui_bg..
-			default.gui_bg_img..
-			default.gui_slots..
 			"box[0,-0.1;3.8,0.5;#c6e8ff]"..
 			"label[1,-0.1;"..minetest.colorize("#000000", title).."]"..
 			help(3.4, -0.1)..
diff --git a/liquids/tank.lua b/liquids/tank.lua
index a2aab49..51dc523 100644
--- a/liquids/tank.lua
+++ b/liquids/tank.lua
@@ -53,6 +53,9 @@ end
 
 local function take_liquid(pos, indir, name, amount)
 	local nvm = techage.get_nvm(pos)
+	if (M(pos):get_int("keep_assignment") or 0) == 1 then
+		amount = math.max(math.min(amount, ((nvm.liquid or {}).amount or 0) - 1), 0)
+	end
 	amount, name = liquid.srv_take(nvm, name, amount)
 	if techage.is_activeformspec(pos) then
 		M(pos):set_string("formspec", techage.liquid.formspec(pos, nvm))
@@ -219,6 +222,9 @@ minetest.register_node("techage:ta4_tank", {
 		if fields.public then
 			M(pos):set_int("public", fields.public == "true" and 1 or 0)
 		end
+		if fields.keep_assignment then
+			M(pos):set_int("keep_assignment", fields.keep_assignment == "true" and 1 or 0)
+		end
 	end,
 	on_timer = node_timer,
 	on_punch = techage.liquid.on_punch,