Fixes RPD/disposals exploits

Also removes a bit of copy-paste and speeds up a helper slightly.

Fixes #13473
Fixes #14654

code/modules/recycling/disposal-construction.dm

@@ -24,8 +24,6 @@
 	..(loc)
 	if(pipe_type)
 		ptype = pipe_type
-		if(!is_pipe())    // bins/chutes/outlets are dense
-			density = 1
 	dir = direction
 
 // update iconstate and dpdir due to dir and type
@@ -199,9 +197,7 @@
 			anchored = 0
 			if(ispipe)
 				level = 2
-				density = 0
-			else
-				density = 1
+			density = 0
 			user << "<span class='notice'>You detach the [nicetype] from the underfloor.</span>"
 		else
 			if(!is_pipe()) // Disposal or outlet
@@ -224,9 +220,7 @@
 			anchored = 1
 			if(ispipe)
 				level = 1 // We don't want disposal bins to disappear under the floors
-				density = 0
-			else
-				density = 1 // We don't want disposal bins or outlets to go density 0
+			density = 0
 			user << "<span class='notice'>You attach the [nicetype] to the underfloor.</span>"
 		playsound(loc, 'sound/items/Ratchet.ogg', 100, 1)
 		update()

code/modules/recycling/disposal-structures.dm

@@ -211,6 +211,9 @@
 //
 /obj/structure/disposalpipe/proc/transfer(obj/structure/disposalholder/H)
 	var/nextdir = nextdir(H.dir)
+	transfer_to_dir(H, nextdir)
+
+/obj/structure/disposalpipe/proc/transfer_to_dir(obj/structure/disposalholder/H, nextdir)
 	H.dir = nextdir
 	var/turf/T = H.nextloc()
 	var/obj/structure/disposalpipe/P = H.findpipe(T)
@@ -222,13 +225,11 @@
 			H.merge(H2)
 
 		H.loc = P
-	else			// if wasn't a pipe, then set loc to turf
-		H.loc = T
+		return P
+	else			// if wasn't a pipe, then they're now in our turf
+		H.loc = get_turf(src)
 		return null
 
-	return P
-
-
 // update the icon_state to reflect hidden status
 /obj/structure/disposalpipe/proc/update()
 	var/turf/T = src.loc
@@ -533,23 +534,7 @@
 
 /obj/structure/disposalpipe/sortjunction/transfer(obj/structure/disposalholder/H)
 	var/nextdir = nextdir(H.dir, H.destinationTag)
-	H.dir = nextdir
-	var/turf/T = H.nextloc()
-	var/obj/structure/disposalpipe/P = H.findpipe(T)
-
-	if(P)
-		// find other holder in next loc, if inactive merge it with current
-		var/obj/structure/disposalholder/H2 = locate() in P
-		if(H2 && !H2.active)
-			H.merge(H2)
-
-		H.loc = P
-	else			// if wasn't a pipe, then set loc to turf
-		H.loc = T
-		return null
-
-	return P
-
+	transfer_to_dir(H, nextdir)
 
 //a three-way junction that sorts objects destined for the mail office mail table (tomail = 1)
 /obj/structure/disposalpipe/wrapsortjunction
@@ -594,26 +579,7 @@
 
 /obj/structure/disposalpipe/wrapsortjunction/transfer(obj/structure/disposalholder/H)
 	var/nextdir = nextdir(H.dir, H.tomail)
-	H.dir = nextdir
-	var/turf/T = H.nextloc()
-	var/obj/structure/disposalpipe/P = H.findpipe(T)
-
-	if(P)
-		// find other holder in next loc, if inactive merge it with current
-		var/obj/structure/disposalholder/H2 = locate() in P
-		if(H2 && !H2.active)
-			H.merge(H2)
-
-		H.loc = P
-	else			// if wasn't a pipe, then set loc to turf
-		H.loc = T
-		return null
-
-	return P
-
-
-
-
+	transfer_to_dir(H, nextdir)
 
 //a trunk joining to a disposal bin or outlet on the same turf
 /obj/structure/disposalpipe/trunk
@@ -701,7 +667,6 @@
 	// transfer to linked object (outlet or bin)
 
 /obj/structure/disposalpipe/trunk/transfer(obj/structure/disposalholder/H)
-
 	if(H.dir == DOWN)		// we just entered from a disposer
 		return ..()		// so do base transfer proc
 	// otherwise, go to the linked object
@@ -715,11 +680,9 @@
 				D.expel(H)	// expel at disposal
 	else
 		if(H)
-			src.expel(H, src.loc, 0)	// expel at turf
+			src.expel(H, get_turf(src), 0)	// expel at turf
 	return null
 
-	// nextdir
-
 /obj/structure/disposalpipe/trunk/nextdir(fromdir)
 	if(fromdir == DOWN)
 		return dir