There are basically two types of colonics...open-system and closed-system. I have had and administered colonics on all sorts of 'machines' and my personal preference is for a closed-system colonic...more water can be used during the session, you release more waste and you are able to relax more. Under the category of closed-systems there are various types of colonics...the Woods Gravity Flow method, Hydrosans, Toxygen, etc. Most of the machines are basically the same from the recipients standpoint...however, the Woods method is different in that it only uses the force of gravity to administer the water...and the control of the water pressure is not done by a dial, but manually by the therapist working with the client. It generally allows for closer contact with the client and the therpaist is able to simultaneously control the water flow and perform abdominal massage (with the other machines the therapist does one and then the other...back and forth...so they usually don't use as much water during the session and don't get as much released). The Woods method...in general...is the older method of doing colonics and is generally not compatible with disposable equipment. HOWEVER....provided the equipment is properly sanitized and disinfected and the speculums are autoclaved...there is NO risk of contamination. Autoclaving is the same procedure used to sanitize surgical, dental, etc. instruments.
As far as what to ask prior to getting a colonic:

Do you have an open- or closed-system? (Your preference determines this...but know beforehand! If you've had one type of colonic and then end up at a facility that has the other...you're likely to be very surprised...and possibly dissapointed!)

Do you use disposable equipment or do you autoclave your speculums? (VERY IMPORTANT...one or the other is a must!)

Do you use purified water? (VERY IMPORTANT...if they say no, take a pass!)

These are the main questions that you need answered. Every therapist has their own style and puts their own twist on doing a colonic...most will do abdominal massage, some will perform reflexology, some use essential oils, some do mini- castor oil packs during the colonic, some offer nutritional consultation as part of the session...some seperately. Regarding probiotics and implants...acidopholus, wheatgrass, coffee, ozone, etc....some facilities will do this and others will not. This does not reflect the quality of the colonic or facility. Introducing anything into the body other than water is considered administering that 'treatment' and has previously been interpreted at 'practicing medicine'...hence it is a felony if the individual is not licensed as a healthcare practitioner. Colon hydrotherapists are NOT licensed in most states and there is no regulation for the industry...so providing this service can leave the facility vulnerable to being shut down and the therapist charged with practicing medicine without a license...that's the felony! Yes, it has happened...so some facilities will not provide probiotics or other implants. However, a good colon hydrotherapist will discuss the importance of probioitcs etc. and may sell them to you so that you can self-administer when you return home. BTW...a growing number of facilities will also require that you insert the speculum yourself...with their guidance...for this same reason. I believe that California is now requiring this.

All that being said...there is considerable difference in the skill and knowledge of one colon hydrotherapist and the next...regardless of the equipment. Your best bet is to ask around at health food stores and alt/com healthcare practitioners (chiropractors, naturopaths, massage therapists...even estheticians and beauty salons) for a referral. If you hear the same name over and over...chances are good that they have a good reputation and loyal following.