I have a splitter that has 3 connections.
One is labeled "Tap". One is labeled "in" and one is labeled "out".
Who/what gets connected to these connections.
I have a TV, a Comcast cable modem (for internet, phone & TV), and a cable box.
Thanks, Hank

You don't have a splitter, you have a tap.

Most people never see a tap. Go get a splitter. It will be labeled in with 2 outs.

These are used in large commercial installations.

The signal levels don't come out evenly distributed.

To use a "tap" for 2 locations. The signal would cone into in of tap #1, the exit on out on tap #1 and into tap #2 in and a 75 ohm terminator would be placed on the Out of tap #2.

Then the connection labeled "tap" would go to each TV.

I believe the modem has an in and out on it. It needs to see the cable first.

Depending on the layout/location of the modem and TV's, you may need one of these: Amazon.com: 2-Port Bi-Directional Cable TV HDTV Amplifier Splitter Signal Booster with Passive Return Path (NOT FOR SATELLITE SYSTEMS): Electronics (http://www.amazon.com/gp/product/B001BMKNZI/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B001HXGZQW&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=08GJW93QMB60XT4Q61TA)

If you really have 3 discrete things to hook up and the cable modem doesn't have an out, then you would need a 4 port bidirectional splitter/amplifer. The 3rd port would have a 75 ohm terminator on it.

If there is just 3 things or really two and I came in an installation kit, then the following would probably work.

Cable from provider into IN of TAP. Out of Tap to cable modem. Assuming modem has no OUT connetor. TAP of the tap goes to the cable box (Cable in). Out of he cable box goes to the TV. TV gets tuned to Ch3 or 4.

Of course its better to use the HDMI connections or Video/audio connections if provided.

HD cable requires a special tuner.

So, basically I'm having trouble with your request:

1. Does modem have an in/out?
2. Was the tap part of an install kit?
3. Are you connecting the cable box to the TV?
3a. What methods are available to you?
4. What kind of tuner or inputs does your tuner have?
5. Is the TV and the cable box one entity? i.e. used together