Sight unseen I would guess that you are using the wrong fittings.

The pipe you are using is made to the SDR (Size dimension ratio) standard while you are attempting to connect it with sched 40 DWV grade fittings which are made to the IPS (iron pipe standard).

SDR pipe is fine for your application but you will need to get SDR fittings to use it.

Where can I buy these SDR fittings? I'll take my pipe sample to verify they work.

I thought there was a 3" standard that worked for everyone.

PVC is used to make pipe for a number of different applications.

PVC pipe intended for "Pressure Piping" is made to ASTM D-1785 and is manufactured to IPS size specifications conforming to IPS sched 20, sched. 40, sched. 80, sched. 120 and sched. 200

Fittings intended for pressure piping will have sharp angles and are identified by the inside diameter of the pipe. All elbows are listed by the change in direction expressed in Degrees. I.E. 90 deg elbow, 45deg elbow, 22.5 deg elbow etc.

PVC pipe intended for use in DWV (drain, Waste & Vent) applications is made to ASTM D-2665 and is only made in IPS sched 40. (Per code, only schedule 40 PVC may be used for DWV applications.)

(Note-sched 40 PVC pipe will normally be labeled under both ASTM 1785 & ASTM D-2665 and can be used for either pressure piping or DWV)

Fittings intended for DWV application will have a radius bend at all changes in direction and they are identied by the fraction of a circle represented by the change in direction. I.E. a DWV grade 90 degree elbow would properly be called a 1/4 Bend and a 45 deg DWV elbow is called an 1/8 Bend, etc.
Tee's and elbows will be prefaced by the term "DWV" or they may be listed as a "Sanitary Tee or Elbow". The may also use the contraction Sani to indicate a DWV fitting such as a 3" Sani-tee.

Code requires that every structure must have a "Main Cleanout" within 3' of the point where the line exits the structure. All drainage and vent lines within the structure are defined as DWV lines (Drain, waste & vent).

The line from the main cleanout to the municipal sewer tap or the septic tank is properly defined as the "House Sewer Line" and any lines intended to convey storm drainage to a Storm Sewer or storm drainage ditch are defined as "Storm Sewers"

When the first started making PVC pipe it was intended to be an alternative to Galvanized Iron Pipe, therefore the pipe is made to the IPS standard, meaning that the pipe size and wall thicknesses compare to the specifications for the metal pipe, hence the use of the IPS standard.

The pipe that you have is intended solely for sewer use, thus it is made to the same standards as set forth for vitreous clay pipe and concrete pipe, that being the SDR (Size dimension Ratio) standard.

Under the SDR standard the thickness of the pipe wall can be determined by dividing the pipe diameter by the index number. By example, you have 3" SDR 30 pipe, which means the actual wall thickness of the pipe is 3" / 30= 0.1".

When you go to your local hardware or home supply store you will find that they have all three types of pipe and fittings but they stock them in different locations to insure they don't get mixed up.

Thanks for the education lazypup.

I went back to home depot and they said they didn't carry the fittings for my pipe. They used to carry it, but not anymore.

They sent me to a specialty plumbing supply place and they didn't carry it either. They didn't offer suggestions as to who else would carry it, but they told me I could use the regular joints and fill them in with putty. I don't know if I want to do this. won't this leak over time?

What does everyone think of using the "regular" joints and doing a massive duct tape job around them?

Your SDR30 pipe is a Hub & Spigot pipe, meaning that it has an expanded end bell (Hub) on one end and just a raw pipe size on the opposite end which is properly called a "spigot end"

For landscape drainage you begin with slotted pipe or pipe with holes in it to absorb the excess water from the soil. The pipe is then laid end to end with the hub on the upstream end and the raw spigot slipped into the hub.

For storm drainage there is no need to glue or seal the joints because the water will follow the path of least resistance through the pipe, and the worst case scenario additional water in the soil will enter the pipe through the loose fitting joints.

If you cannot find the correct SDR fittings for storm and landscape drainage you may use PVC sched.40 fittings and just loose slip fit them.

Regardless of the purpose or the wall thickness the fittings and pipes should fit together. Inside diameter SHOULD be the same. I'm having the same problem on a project I'm doing.