obleyo, your client should have hired an architect instead of taking the cheap route.

You should at least know where the plumbing is going through, it isn't your job to know the optimal routing of the plumbing. Usually for large projects an MEP engineer is involved early on, from experience. I have never done small houses so can't comment on that.

^ adequate room for chase walls for stacks and venting is the bare minimum.

A good designer should know more than this in order to control the project's systems thou.

Unless you are doing some monster house or your local plan check agency requires it - plumbing is usually design build - locate the fixtures on your plans and the GC and pluming sub will just figure it out in the field - That being said, it is good to know the basics on supply/waste line and venting so you are proposing something that can actually work.   

agree w/ above.  

if the guy is building a giant f'ing addition then i'd be concerned about not hiring an architect, but for most residential additions, who cares.  I have to believe that most residential projects are probably more trouble than their worth - tiny fee, lots of hand holding, many changes. etc.

hope this doesn't mean that you've given up acting

This forum can be rough for designers and non registered "architects". Lol   Quite frankly a renovation would have been a better start for you, a kitchen a bathroom, as opposed to a project that requires you to be responsible for the building's envelope given your experience. None the less look on amazon for ref books. I bought books for my niece called "residential design and drafting" as well as residential construction academy books. These should help you out. PLEASE read the IRC and don't go beyond its boundaries. Good luck to you and the homeowner. I would also recommend that you hire a "project architect" to assist. Not all architects are designers, some are technical experts and managers and are more than willing to work with designers.

Full blown additions, imho, are the toughest small residential projects out there. From a constructability standpoint, you have all the problems of new construction plus all the problems of remodeling plus the joint. How well you need to know plumbing depends on how developed the client wants your drawings to be. Usually, you have to guide them to figure that out. Do it yourself and risk fucking the whole thing or hire someone who knows what they are doing and have a solid project and learning experience...

Shit flows downhill.

Yes, you need to identify all plumbing requirements and reflect them in your tender drawings (location, specifications, intent).

If you leave them to your plumber, he will decide for you and he will supersede all your "artistic" intents since he will do whatever is going to be easiest for him.

First thing off, when going for plan check you will be required to submit STAMPED plans from a licenced architect, also structural calcs must be signed by a professional SE.

The county of LA used to be lenient with remodels/expansions which is no longer the case. You will be forced to "parner" with a professional and assume your earnings to go down the drain but can be used as an experience. Your call. 

In actually plumbing dwgs are rather easy,  study proper location of plumbing walls, fixture isomentrics, and how are you tying back to main discharge/cleanout trap (min diameter. 2% min slope etc etc) 

Ps: I live in socal and have worked many times with LA & surrounding counties.