First of all, thank you for calling them 8p8c connectors rather than the more common but incorrect name of RJ-45.
Unfortunately, the wiring all depends on what is meant by tx and rx which is not as obvious as it sounds. Strictly speaking RS-232 only applies to the connection on a modem, any other use of the standard (even the computer end of a modem cable) is just by analogy.
Definition 1: one way of looking at it is to consider data coming out of a box as being transmitted and data going into it as being received.
Definition 2: the other way is to think of data going from the computer to the modem (and, by analogy, any other box) as being transmitted and data from the modem to the computer as being received.
These are different on a modem where transmitted data (definition 1) is actually received by the box (definition 2).
So what you need to determine is which definitions of tx and rx the person who defined the 8P8C connections you are using: do they mean tx as transmitted from the computer to the thingy or vice-versa. For the 25-pin female submin D connector on a computer serial port it's not so complicated: tx is the data coming out of the computer and rx is data going into it.
You write:
On the serial connector tx and rs are pins 2&3
This is true on a 25-pin connector (true RS-232). The most common connectors these days is a 9-pin (variously known as AT serial, because it was first commonly used on the IBM PC-AT, or RS-574) where tx and rx are pins 3 & 2 (i.e., same pin numbers but opposite order from a 25-pin connector - I always have to look up which is which).
On the 8p8c connectors 5&6 are the tx and rx.
That sounds like they're using the definition of tx is data coming out of the box and rx is data going into it. I say this because the
EIA/TIA - 561 standard has RD on 5 and TD on 6 which would be by the definition of data flowing to and from the modem so it appears that the definition in use here is of data flowing into and out of the box.
Here's what I'd do: measure the voltage on the 8P8C pins 5 & 6. The one that's high (probably about minus 6 to 10 volts) is transmit data (out of the box). I'd connect that to the computer's receive data pin (pin 3 on a 25-pin connector, pin 2 on a 9-pin connector). The other pin will probably show a lowish positive voltage (maybe about plus 2 volts) or even not have any voltage. Connect that to the computer's transmit data pin (pin 2 on a 25-pin connector, pin 3 on a 9-pin).
If you get it wrong it shouldn't matter even if you have two transmit pins pulling in opposite directions on the same wire. RS-232 says that transmitters are supposed to be safe with that.
