Waste

Waste (called "waste product" on some screens of the game) is a game currency. It is spent to recruit Drowners.
Waste comes from several sources:
* Recycling gems, souls, or raw mana.
* From using the energy crystals.
* A reward for resetting by blowing up a boiler.
* The spell Aegis of the Plague.
* Accretion over time (including off-line time), very slowly.
* Day 9 of the search cycle in the Junkyard.
* The mushroom farm.
Waste is harder to acquire in large quantities than gems, souls and raw mana. Even dark mana is easier to get once Warlocks are unlocked. Thus, waste can limit a players progress and some forward planning is needed to manage it. In particular, if a player resets using the Obelisk, rather than resetting by blowing up a boiler, no waste is awarded. It might be useful to plan short runs after Obelisk resets and longer ones after boiler resets.
Aegis of the plague gives a decent amount of waste, but in a way that essentially ends a run and requires an immediate reset. It is not clear how this spell could best be exploited.
The mushroom farm initially yields rather modest amounts of waste (via rotted Dark mushrooms, 1,500 waste each, limited by availability of Magic Powder). The yield can be improved by some Undead contracts. Bubonic mushrooms, which need Essence to grow, give much more waste.
== A waste-management strategy ==
This is an attempt to get a useful number of Drowners out of a limited supply of waste. It works fairly well at the point where the supply of raw mana starts to limit progress. There may be better ways, especially in later stages of the game.
This strategy assumes that daemon contract D, which enhances the energy crystals, is at least at level 3, levels 4 or 5 being preferred. It's too slow without the energy boost.
# Do a moderately-deep run and reset using boiler A to get maximum waste; around 1e5 waste is good. Alternatively, start the run just after getting 1e5 waste from the Junkyard search.
# Recruit only enough Drowners in each rank to get one of the next rank up.
# Don't upgrade drowners of a given rank until they are being supplied by the next rank up.
# When there are enough gems to recruit Mavka, recruit no more than 50 Mavka, even though there is enough waste for many more.
# When the daemons have supplied ~1e152 gems, unlock crystal 5, the one that yields dark mana.
# Use crystal 5 in preference to other crystals until you have 600 dark mana. Then unlock the cheapest spot in the Grimoire (100 mana), and the spell The energy circle (500 mana). This speeds up the crystals significantly.
# Go on using crystal 5 until you have 300 more dark mana. Spend 250 to unlock the second spot in the Grimoire and 50 to unlock the spell Swamp ritual which recruits ~1 Mavka per second for free.
# Speed up the Mavkacation programme using crystal 2 until you have enough of them to recruit Dagon.
# Use the rest of your saved waste to recruit Dagon.
Step 6 is optional. It delays getting the free Mavka and the extra raw mana, but speeds up the wider process of exploiting Warlocks which is the normal arc of a run.
This strategy runs out of power before being able to recruit any Kelpie and the run will ultimately slow right down due to shortage of raw mana relative to the other resources. However, it does get one a fair way into a long run.